It's not the most glamorous field for entrepreneurs -- selling into the existing education industry is a nightmare -- but it's potentially lucrative, and doing good work here means potentially changing the world in a meaningful way.

So there's no shortage of education and learning startups. Here are some of our favorites.

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Chegg

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"Netflix for textbooks" boasts "at least one customer from well over 7,000 of the 8,000 higher education campuses in the U.S." according to a recent AdAge article.

Knewton

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"Adaptive learning" company -- where each student gets a personalized curriculum based on their skills and level.

As the company explains... "Knewton analyzes learning materials based on thousands of data points—concepts, structure, difficulty level, media format—and uses sophisticated algorithms to piece together the perfect bundle of content for each student, every day."

Kno

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Kno started as a tablet company but is now focusing on e-textbooks, boasting 100,000 in its store at 30% to 50% off list price. Its opportunity is to capitalize on the growth of iPads and Kindles that are being brought into the classroom.

General Assembly

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This NYC-based facility is more than just office space and community for hot startups. General Assembly also offers courses -- taught by local experts -- on topics ranging from business ("Nailing The Pitch" and "Starting Up in China") to design ("Best/Worst Brand Bootcamp") to programming. Next up: A London bureau.

Quora

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Learning is as much about resources as it is about the educational process, and Quora has become one of the web's leading question-and-answer sites for smart, intellectual topics. See also: Stack Exchange.

Encore Career Institute

Imagine K12

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It's not just one startup -- it's an entire incubator for education-related companies. The pitch: "Over a three month period, we will draw on our extensive entrepreneurial experience, understanding of the Silicon Valley ecosystem, and knowledge of the education industry to help bring your idea to life, get your company funded, and to get your company on the road to success."

Mixel

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One of the most important roles that technology can play -- especially as budgets keep getting cut -- is to extend arts education. The iPad in particular -- an easy-to-use, touch-driven computer -- is perfect for that. So we'd love to see room for apps like Mixel -- a collage and art-remixing app -- somehow find a role in education.